Proposition 37 could make California the first state in the country to require labels on foods made with genetically-modified ingredients. It’s shaping up to be one of the most contentious — and certainly the most expensive — battles on the state’s November ballot.

On one side are organic food groups that have spent about $3 million in support of the labeling law. On the other are biotech firms like Monsanto and food giants including Pepsi, Sara Lee, and General Mills, which have contributed upwards of $28 million to try and keep GMO labels off food packages.

If Proposition 37 passes, you’ll see a change in nearly every part of the grocery store.

To the “No On 37″ camp, there is nothing benign about a label

Take the cereal aisle, where Stacy Malkan with the “Yes on 37” campaign recently picked up a box of granola and pointed to the ingredients panel.

“Many of these products have corn syrup, cornstarch, sugar beets, and soy products that are genetically engineered,” she said.

In the United States, up to 90 percent of those foods are grown from seeds that have been genetically modified. Scientists made changes in the plants’ DNA to make the crop resist pests or stay fresh longer, to name two examples.

“It’s not a warning sticker,” she says. “[It’s not] a skull and crossbones or anything. It’s literally just a few words added to existing labels, just indicating [the food was] partially produced with genetic engineering.

But to the “No On 37″ camp, there is nothing benign about a label.

Take, for instance, Kent Bradford, a professor of plant science at the University of California, Davis and director of its Seed Biotechnology Center.

Bradford’s team works with — among other plants — lettuce.

California supplies 80 percent of the nation’s lettuce. But growers here, he says, increasingly find themselves at odds with a fact of nature.

Lettuce, he says, evolved for a Mediterranean climate. Its seeds lay dormant when it’s hot and germinate when it rains.

But it’s getting hotter here in California — and farmers want to be able to grow lettuce year-round, not just when it rains. So Bradford’s team is developing a new kind of lettuce seed.

He points to several strands of straggly, stringy lettuce. At this overgrown stage, it’s not appetizing-looking produce. But Bradford says these plants could help farmers adapt to a changing climate.

“What we’ve identified here is if we turn off this one gene, it eliminates that mechanism of inability to germinate at high temperature,” he says.

GM isn’t an ingredient, it’s a technology

Part of what bothers Bradford about Proposition 37 is that genetic modification isn’t an ingredient, like saturated fat. It’s a technology, one capable of creating countless variations on nature, some of them potentially very useful.

“You wouldn’t want to label a screwdriver as dangerous just because someone might poke it through their hand or something,” he explained.

Bradford fears that if Prop 37 passes, consumers will regard those GMO label as a scarlet letter, a signal that the entire technology is flawed and dangerous.

“Why would they be putting this on the label if it weren’t something I should be concerned about,” he imagined consumers asking themselves.

Indeed, that’s the question many consumers have about genetically modified foods: Are they safe?

Is GM safe? Grappling with a scarcity of science

Unfortunately, the body of peer-reviewed research on GM foods is tiny, consisting of a handful of small studies done on mice. Some of these studies suggest possible links to immune-system impairment and other problems. Compared to the amount of research done on, for instance, BPA, it’s a drop in the bucket.

Both the American Medical Association and the FDA say that genetically-modified foods are safe to eat and do not need to be labeled.

But Prop. 37 advocates and critics of GM foods say the fact that the science is nascent only underscores the need for greater regulation and labeling.

They say the process of genetic engineering can be imprecise and that plant scientists may not always know the full, long-term implications of the crops they develop.

“The jury is still out on the health effects,” says Yes on 37’s Stacy Malkan. “And in many ways, the evidence hasn’t even been presented.”

Such concerns are widespread in Europe, where GM labeling is mandatory. But that’s also increasingly the case in California, where a recent poll found 65 percent of voters planning to support Prop. 37.

Here in the states, at least, it wasn’t always this way.

We’ve been here before: The lesson of the Flavr Savr tomato

Belinda Martineau was a plant scientist at the Davis-based biotech firm Calgene in the late 1980s and early 90s. She was part of the team that helped invent the Flavr Savr tomato, the world’s first commercially-available genetically modified whole food.

Martineau says she and others at Calgene weren’t sure how the Flavr Savr was going to go over with the public.

“Jurassic Park came out while we were readying the tomato for the marketplace,” she recalls. “We were worried about it. We were worried about the public’s perception.”

So Calgene made a choice: total transparency. The Flavr Savr wasn’t just labeled, it came with a brochure shaped like a tomato.

“It actually explained the genetic engineering technology in lay terms that people could understand … And it had a 1-800 number, in case people wanted to learn more.”

No laws required that Calgene label the tomato. Martineau says the company wanted to label the Flavr Savr because they were proud of it.

“We wanted to be transparent”

“We believed in what we were doing. We thought if we were careful about it and transparent that we could convince the public that they should be as enthusiastic about it as we were.”

And shoppers were enthusiastic. In Davis, where Martineau lives, Flavr Savrs flew off the shelves.

“They had a policy at the local IGA that you could only purchase two Flavr Savor tomatoes per person, per day,” says Martineau. “How they kept track of that, I don’t know.”

What ultimately killed the Flavr Savr wasn’t the public’s fear of genetic engineering. It was the technology itself. Flavr Savrs didn’t taste better than regular tomatoes and they were too difficult to transport.

For Martineau, there’s a lesson here. Not labeling, she says, makes the industry look like it has something to hide. She believes labeling is an opportunity.

“This is one of the best ways the industry can turn public opinion around, is to be honest, to be transparent. And to come out and be proud of their products.”

If Proposition 37 passes on November 6, the question is whether the public will see those labels the same way Martineau does.